The present invention is directed to a printing device. The printed device has a plurality of print heads, each of which has a printing area.
The printing device is provided with a plurality of print heads, each of which has a printing area whose extension, in the printing direction, fixes a line height, and whose extension transversely to the printing direction fixes a column width. The print heads are arranged in several parallel rows that are spaced apart from each other. The print heads of different rows are offset transversely to the printing direction in respect to each other.
The term xe2x80x9cprint directionxe2x80x9d in this context means the movement direction of the material to be imprinted relative to the print heads. If printing plates mounted on rotating printing plate cylinders are provided as the material to be imprinted, the print direction extends perpendicularly in respect to the axis of rotation of the printing plate cylinder.
Printing devices of this general type are employed for placing images on offset printing plates, for example. A coating material, or in the inverse situation, a solvent for dissolving a coating of the printing plate, can be sprayed on the latter by operation of the plurality of print heads.
In order to obtain a printed image of high quality, it is desirable to be able to apply the medium to be applied to the printing plates finely and evenly distributed to each area of the printing plate and without missing any spots. For this purpose, the print heads must be sufficiently closely aligned in relation to each other. On the other hand, the possible density for packing the print heads close to each other is limited, since they touch each other. It would therefore be desirable to make do with as few print heads as possible.
U.S. Pat. No. 5,719,602 shows an ink jet print head with a multitude of nozzle groups. These nozzle groups are arranged offset in respect to each other.
DE 37 30 844 A1 discloses a matrix ink printer. Several print heads, each with several nozzle openings, are arranged offset in relation to each other. In this case, the nozzle openings overlap in relation to the material to be imprinted.
The object of the present invention is based on providing a printing device.
In accordance with the present invention, this object is attained by the provision of a printing device with a plurality of print heads. Each of these print heads has a printing area. An extension of each printing area in the printing direction fixes a line height. An extension of each printing area transverse to the printing direction fixes a column width. The print heads are arranged in several parallel rows and the print heads in different rows are offset transversely to each other in the printing direction. The spacing of the print heads in each print head row corresponds to the column width times the number of rows. The distance of the rows from each other corresponds to the line height times the number of rows increased by one.
The advantages which can be obtained by the present invention lie, in particular, in that the spacing distance of the print heads in one print head row corresponds to the column width times the number of rows. The distance of the rows from each other corresponds to the line height times the number of rows increased by one. The column jumps in a print head row correspond to the number of print head rows, while the line jumps between adjoining print head rows are greater by one than the number of print head rows in the printing device. The print heads are arranged with such accuracy that no gaps and no overlaps between the print heads, in areas where no printing, or double printing would occur, are provided. Accordingly, a high degree of resolution, with a simultaneous compact construction of the printing device, can be achieved.
In an advantageous manner, the print heads of several rows are arranged in a common plane. Specifically, one print head from one row can lie on a common plane with a corresponding print head in every other row. The assembly of the individual print heads is made considerably easier. They can, in particular, be fastened on a level print head holder. Besides a compact arrangement, it is also possible, in this way, to achieve a simple alignment capability of the print heads in relation to each other.
In accordance with a further development of the present invention, the individual print heads are arranged obliquely with respect to the print direction in order to achieve a higher resolution. Each printing head has a longitudinal direction which is determined by its print area, or by the line along which the nozzle openings are arranged. The print heads are arranged obliquely, in respect to the print direction, in such a way that the longitudinal direction for each print head extends at an acute angle to the print direction. That acute angle can be matched to the existing circumstances, and in particular can be matched to the shape of the print heads. In accordance with an embodiment of the present invention, the angle can lie between 20xc2x0 and 45xc2x0, and in particular can be approximately 30xc2x0.
In a further development of the present invention, the print heads from the different rows are placed obliquely by the same angle with respect to the print direction. In particular, they can be arranged in such a way that the longitudinal directions of the print heads of different rows lie on a common plane. The common plane is inclined in relation to the print direction by the same angle by which the print heads are placed obliquely to the print direction.